chert_synonym.cc

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/* Copyright (C) 2004,2005,2006,2007,2008,2009,2011 Olly Betts
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
 */

#include <config.h>
#include "chert_synonym.h"

#include "xapian/error.h"

#include "chert_cursor.h"
#include "debuglog.h"
#include "stringutils.h"
#include "api/vectortermlist.h"

#include <set>
#include <string>
#include <vector>

using namespace std;

// We XOR the length values with this so that they are more likely to coincide
// with lower case ASCII letters, which are likely to be common.  This means
// that zlib should do a better job of compressing tag values.
#define MAGIC_XOR_VALUE 96

void
ChertSynonymTable::merge_changes()
{
    if (last_term.empty()) return;

    if (last_synonyms.empty()) {
        del(last_term);
    } else {
        string tag;

        set<string>::const_iterator i;
        for (i = last_synonyms.begin(); i != last_synonyms.end(); ++i) {
            const string & synonym = *i;
            tag += uint8_t(synonym.size() ^ MAGIC_XOR_VALUE);
            tag += synonym;
        }

        add(last_term, tag);
        last_synonyms.clear();
    }
    last_term.resize(0);
}

void
ChertSynonymTable::add_synonym(const string & term, const string & synonym)
{
    if (last_term != term) {
        merge_changes();
        last_term = term;

        string tag;
        if (get_exact_entry(term, tag)) {
            const char * p = tag.data();
            const char * end = p + tag.size();
            while (p != end) {
                size_t len;
                if (p == end ||
                    (len = uint8_t(*p) ^ MAGIC_XOR_VALUE) >= size_t(end - p))
                    throw Xapian::DatabaseCorruptError("Bad synonym data");
                ++p;
                last_synonyms.insert(string(p, len));
                p += len;
            }
        }
    }

    last_synonyms.insert(synonym);
}

void
ChertSynonymTable::remove_synonym(const string & term, const string & synonym)
{
    if (last_term != term) {
        merge_changes();
        last_term = term;

        string tag;
        if (get_exact_entry(term, tag)) {
            const char * p = tag.data();
            const char * end = p + tag.size();
            while (p != end) {
                size_t len;
                if (p == end ||
                    (len = uint8_t(*p) ^ MAGIC_XOR_VALUE) >= size_t(end - p))
                    throw Xapian::DatabaseCorruptError("Bad synonym data");
                ++p;
                last_synonyms.insert(string(p, len));
                p += len;
            }
        }
    }

    last_synonyms.erase(synonym);
}

void
ChertSynonymTable::clear_synonyms(const string & term)
{
    // We don't actually ever need to merge_changes() here, but it's quite
    // likely that someone might clear_synonyms() and then add_synonym() for
    // the same term.  The alternative we could otherwise optimise for (modify
    // synonyms for a term, then clear those for another, then modify those for
    // the first term again) seems much less likely.
    if (last_term == term) {
        last_synonyms.clear();
    } else {
        merge_changes();
        last_term = term;
    }
}

TermList *
ChertSynonymTable::open_termlist(const string & term)
{
    vector<string> synonyms;

    if (last_term == term) {
        if (last_synonyms.empty()) return NULL;

        synonyms.reserve(last_synonyms.size());
        set<string>::const_iterator i;
        for (i = last_synonyms.begin(); i != last_synonyms.end(); ++i) {
            synonyms.push_back(*i);
        }
    } else {
        string tag;
        if (!get_exact_entry(term, tag)) return NULL;

        const char * p = tag.data();
        const char * end = p + tag.size();
        while (p != end) {
            size_t len;
            if (p == end ||
                (len = uint8_t(*p) ^ MAGIC_XOR_VALUE) >= size_t(end - p))
                throw Xapian::DatabaseCorruptError("Bad synonym data");
            ++p;
            synonyms.push_back(string(p, len));
            p += len;
        }
    }

    return new VectorTermList(synonyms.begin(), synonyms.end());
}


ChertSynonymTermList::~ChertSynonymTermList()
{
    LOGCALL_DTOR(DB, "ChertSynonymTermList");
    delete cursor;
}

string
ChertSynonymTermList::get_termname() const
{
    LOGCALL(DB, string, "ChertSynonymTermList::get_termname", NO_ARGS);
    Assert(cursor);
    Assert(!cursor->current_key.empty());
    Assert(!at_end());
    RETURN(cursor->current_key);
}

Xapian::doccount
ChertSynonymTermList::get_termfreq() const
{
    throw Xapian::InvalidOperationError("ChertSynonymTermList::get_termfreq() not meaningful");
}

TermList *
ChertSynonymTermList::next()
{
    LOGCALL(DB, TermList *, "ChertSynonymTermList::next", NO_ARGS);
    Assert(!at_end());

    cursor->next();
    if (!cursor->after_end() && !startswith(cursor->current_key, prefix)) {
        // We've reached the end of the prefixed terms.
        cursor->to_end();
    }

    RETURN(NULL);
}

TermList *
ChertSynonymTermList::skip_to(const string &tname)
{
    LOGCALL(DB, TermList *, "ChertSynonymTermList::skip_to", tname);
    Assert(!at_end());

    if (!cursor->find_entry_ge(tname)) {
        // The exact term we asked for isn't there, so check if the next
        // term after it also has the right prefix.
        if (!cursor->after_end() && !startswith(cursor->current_key, prefix)) {
            // We've reached the end of the prefixed terms.
            cursor->to_end();
        }
    }
    RETURN(NULL);
}

bool
ChertSynonymTermList::at_end() const
{
    LOGCALL(DB, bool, "ChertSynonymTermList::at_end", NO_ARGS);
    RETURN(cursor->after_end());
}